1. Field of the Invention
The present invention relates to an improvement in an image pickup device using a solid-state image pickup element having a nonuniform sensitivity within one pixel.
2. Related Background Art
In recent years, solid-state image pickup elements have been increasingly developed due to their many advantages as compared with camera tubes.
FIG. 1 is a schematic view of a conventional image pickup device using a solid-state image pickup element of this type, and particularly, shows a pixel structure of a solid-state image pickup element A. This structure includes a polysilicon electrode 1 connected to an electrode of a drive signal .phi.1, an oxide film (insulating film) 2, and a virtual electrode 3. FIG. 2 is a chart showing a potential of the solid-state image pickup element A in FIG. 1. Arrows in FIG. 2 represent the moving directions of charges.
An operation of the above structure will be described below. In a charge accumulation mode, the polysilicon electrode 1 is set at a low voltage by the drive signal .phi.1, thereby obtaining a potential indicated by the solid line in FIG. 2. Therefore, a charge is accumulated under the virtual electrode 3.
In a charge transfer mode, high and low voltages are alternately applied to the polysilicon electrode 1. The accumulated charges are then sequentially transferred.
This solid-state image pickup element A has a so-called virtual phase (virtual electrode) structure. A single-phase vertical transfer pulse can be used, and only a simple structure is required. Therefore, the virtual phase structure is widespread.
In the conventional image pickup device, however, since the polysilicon electrode absorbs light components having short wavelengths, the sensitivity during charge accumulation cannot be uniformed within one pixel. For this reason, a false signal component is undesirably contained in a video signal, thereby degrading quality of a reproduced image.